The friction behaviors of CVD diamond films on silicon nitride substrates are investigated comparing with the uncoated silicon nitride samples. Two types of CVD diamond films, namely MCD and NCD films, are deposited on the silicon nitride substrates using HFCVD method, and then SEM, while light interferometer, XRD and Raman spectra are employed to characterize as-deposited diamond films. The friction tests are carried out in a ball-on-plate reciprocating friction tester, with ball-bearing steel, copper, tungsten carbide and tungsten carbide as the counterpart materials. The results show that the diamond film deposited on silicon nitride substrate has significant effect on reducing the friction coefficient and enhancing the wear resistance. The friction coefficients of MCD and NCD films are around ~0.35 in dry sliding against ball-bearing steel and copper, while for sliding with the tungsten carbide and silicon nitride, the friction coefficients of NCD films even decrease as low as ~0.12 and ~0.08 respectively. The special wear rate of the silicon nitride and NCD film can be estimated as 6.2167×10-5 mm3 N-1 m-1 and 4.03×10-7 mm3 N-1 m-1 with the counterface of silicon nitride. Comparatively, no measurable wear occurs on the worn surface of the MCD film.